The sport of running is a popular fitness activity, with an estimated 30 million Americans classified as recreational runners (Austin, 2002). The overall incidence of lower extremity injuries in runners that run≧5 km per training day or race has been found to range between 19.4% and 79.3% (van Gent et al., 2007). The predominant joint injured is the knee (7.2% to 50.0%) followed by the ankle (3.9% to 16.6%) and hip (3.3% to 11.5%). Overuse injuries are the majority of all musculoskeletal running injuries stemming from training errors, anatomical or biomechanical factors (Hreljac et al., 2000; James et al., 1978; Macera et al., 1989).
Core stability has been defined as the lumbo-pelvic hip muscle strength and endurance yielding a coordinated activation of muscles and maintenance of alignment throughout the kinetic chain (Fredericson et al. (2005); Kibler et al. (2006); Leetun et al. (2004); Willson et al. (2005)). The stance phase of running is a closed kinetic chain activity requiring proximal stability to balance and support the weight of the upper body. When core instability exists, due to strength and/or endurance deficits, the body may not be optimally aligned to absorb and produce large ground reaction forces, which in turn could place the runner at an increased risk for lower extremity injury (Ferber et al., 2002; Marti et al., 1988). Frontal plane pelvic drop is one sign of core instability that could be identified as a weak link in the kinetic chain. Pelvic drop in the frontal plane, termed ‘Trendelenburg gait,’ is visualized when there is a downward obliquity from the hip of the stance leg towards the opposite hip during its swing phase. It should be understood that the term “kinetic chain” or “kinetic chain of joints” are terms borrowed from engineering, and are used in reference to a combination of successively arranged joints in which the terminal segment may move freely, such as when throwing a ball, or when the terminal joint is fixed, such as when performing a push-up.
Core instability as demonstrated by frontal plane pelvic drop is due to strength and endurance issues of the gluteus medius muscle (Mann et al., 1986). The gluteus medius is one of the strongest lower extremity muscles (Ward, Eng, Smallwood, & Lieber, 2009) and is made up of three parts of nearly equal volume with three distinct muscle fiber directions and separate innervations (Dostal, Soderberg, & Andrews, 1986; Gottschalk, Kourosh, & Leveau, 1989). This muscle originates on the dorsal ilium below the iliac crest and inserts at the top outside surfaces of the greater trochanter. Based on its anatomical location, cross sectional area and architecture, the gluteus medius muscle is critical to the functions of the lower back (Nelson-Wong, Gregory, Winter, & Callaghan, 2008), hip (Bolgla & Uhl, 2005; Delp et al., 1999), knee (Boling, Bolgla, Mattacola, Uhl, & Hosey, 2006; Mascal, Landel, & Powers, 2003; Nakagawa et al., 2008) and the ankle. Hence, core instability due to gluteus medius muscle weakness will lead to abnormal spinal and lower extremity kinematics during running.
The gait adaptations due to a weak or fatigued gluteus medius muscle during running and the anatomical areas at risk of structural overload are summarized in Table 1 (Bolgla & Uhl, 2005; Boling, Bolgla, Mattacola, Uhl, & Hosey, 2006; Cichanowski et al., 2007; Fredericson et al., 2000; Ireland et al., 2003; Leetun et al., 2004; Mascal, Landel, & Powers, 2003; Nakagawa et al., 2008; Nelson-Wong, Gregory, Winter, & Callaghan, 2008; Niemuth et al., 2005; Presswood et al., 2008; Reiman et al., 2009; Souza et al., 2009). Individual running techniques may demonstrate combinations of the adaptations below but clearly not simultaneous medial and lateral knee drift. Further, the gait adaptations may also occur during walking visualized as a waddling motion or a limp.
The following listing shows gait adaptations due to a weak gluteus medius muscle during running. A Trendelenburg gait is associated with a risk of structural overload in the lumbar spine, sacroiliac joint (SIJ), and greater trochanter bursa, as well as an insertion of muscle on the greater trochanter, and overactivity of the piriformis and tensor fascia lata (TFL). Medial knee drift (valgus position of tibiofemoral joint) is associated with structural overload in the lateral tibiofemoral compartment (via compression), patellofemoral joint, patella tendon and fat pad, pes anserinus, iliotibial band (ITB), and anterior cruciate ligament strain (ACL). Lateral knee drift (varus position of tibiofemoral joint) is associated with structural overload in the medial tibiofemoral compartment (via compression), ITB, posterolateral knee soft tissues (via tension), and popliteus. A same sided shift of trunk (lateral flexion of trunk) is associated with structural overload in the lumbar spine (increased disc and facet joint compression), and SIJ (increased shear).
The most commonly diagnosed lower limb soft tissue injuries caused by distance running are iliotibial band syndrome, tibial stress syndrome, patellofemoral pain syndrome, Achilles tendonitis and plantar fasciitis (Yeung & Yeung 2001). From the table above, a common adaptation from weakness of the gluteus medius muscle during the stance phase of running occurs when the femur excessively adducts or internally rotates. These motions increases the tension on the iliotibial band (Taunton et al., 2002) and cause abnormal patellofemoral contact stress (Souza & Powers, 2009). Continuing down the kinetic chain, internal rotation of the femur also allows the knee to fall into a valgus position and promotes the tibia to rotate internally relative to the foot and increases the weight transfer to the medial aspect of the foot. These motions increase the risk of any condition relating to excessive and/or prolonged pronation of the foot such as tibial stress syndrome and Achilles tendonitis (Lundberg et al., 1989). Further, the combination motions of ankle pronation and knee valgus are implicated as the primary mechanism of non-contact ACL injury in sports where running is an integral component (Souza & Powers, 2009).
Poor lumbo-pelvic posture due to abnormal sagittal plane or frontal plane pelvic rotations leads to compensation in the thoracic spinal posture and subsequent shoulder dyskinesis (Borstad, 2006; Greenfield et al., 1995). Poor thoracic posture relates to an increased forward curve of the thoracic region of the spine (kyphosis) and produces a ‘hunching’ or ‘hump back’ appearance and a rounding of the shoulders. The rounding of the upper back and shoulders cause the head and neck to tilt downward thus to look straight ahead requires the head to be lifted upward and forward. This forward head posture causes several clinical symptoms and also the continuation of many clinical issues including headaches, pain between the shoulder blades, upper back pain, neck pain, numbness and tingling of the fingers and shoulder pain. Pain originating from the shoulder could also radiate into the neck, head, arm, or chest.
Excessive rounding of the shoulders disrupts the upper kinetic chain during arm raising movements and causes a sequence of abnormal kinematic events of the scapula, clavicle and humerus. First, this thoracic kyphosis causes abnormal three-dimensional scapular kinematics including abnormal scapular protraction, internal rotation, downward rotation and anterior tilting. These abnormal motions produce shoulder pain and glenohumeral joint movement dysfunction common to many debilitating conditions discussed below. The most frequently occurring problems include shoulder impingement and associated rotator cuff disease or tendinopathy, which can progress to rotator cuff tears as well as glenohumeral joint instability and adhesive capsulitis. A very high proportion of these shoulder complaints are related to occupational or athletic activities that involve frequent use of the arm at, or above shoulder level.
The following provides a summary of scapular kinematics when raising the arm in healthy and pathological states (modified from Ludewig and Reynolds, 2009). The muscle group associated with primary scapular motion has an upward rotation when healthy. When impingement or rotator cuff disease and/or glenohumeral joint instability are present, the muscle group exhibits less upward rotation. When adhesive capsulitis is present, the group exhibits greater upward rotation. The muscle group associated with secondary scapular motion exhibits a posterior tilting when healthy. When impingement or rotator cuff disease are present, less posterior tilting is exhibited. No consistent evidence for motion alteration has been found in the cases of glenohumeral joint instability and adhesive capsulitis. The muscle group associated with accessory scapular motion exhibits internal and external rotation when healthy. The muscle group exhibits greater internal rotation when impingement or rotator cuff disease and/or glenohumeral joint instability are present; however a consistent response has not been shown in the case of adhesive capsulitis. When all of the muscle groups are in a healthy state, the shoulder range of motion and subacromial space are maximized. Impingement or rotator cuff disease is contributory to subacromial or internal impingement, while glenohumeral joint instability is contributory to less inferior and anterior joint instability. Adhesive capsulitis results in compensation to minimize a loss in the functional range of motion.
Thoracic kyphosis and abnormal scapular kinematics changes the resting length and sensory capacity of 17 muscles that attach to the scapula: serratus anterior, supraspinatus, subscapularis, trapezius, teres major, teres minor, triceps (long head), biceps brachii, rhomboid major, rhomboid minor, coracobrachialis, omohyoid, latissimus dorsi, deltoid, levator scapulae, infraspinatus and pectoralis minor. The tension within these 17 muscles produce a balance of forces across the scapula. A positional change of the scapula will cause a lengthening and a shortening of opposing muscles attached to the scapula that disrupts this muscular balance leading to a reduction of the force generating capacity of muscles and limiting the functional stability and mobility of the shoulder. Further, each muscle has sensory receptors that inform the central nervous system of the length and tension state of the muscle as well as the position of a joint or bone. The quality of this sensory information is reduced with abnormal scapular motion and either causes or compounds movement compensations and clinical symptoms of the glenohumeral joint.
The scapula and the muscles attaching to the scapula are also a part of the fascial networks of the body. Fascia, in general, is a connective tissue that encases muscles (and organs) and attaches them to the skeletal system. Muscles (latin: myo) and their connective tissue form functional myofascial lines of the body which ultimately construct the kinetic chain. The scapula is an important intersection of several myofascial tracks, or continuities of myofascial units that integrate the axial skeleton (arms and legs) with the trunk. Fascia is a material that can deform and retain its length when it is either shortened or lengthened hence abnormal scapular positions influence the myofasical tracks of the entire body that influence postural function and movement based problems.
Last, the upper arm, or humerus, articulates with the scapula at the glenohumeral joint and abnormal scapular kinematics from poor shoulder posture causes the humerus to shift down and rotate inwards toward the center of the body. The scapula also articulates with the clavicle at the acromioclavicular joint hence abnormal scapular and humeral kinematics causes abnormal clavicular kinematics, namely clavicular protraction, and increases force transmission of the proximal portion of the clavicle on the first rib at the sternoclavicular joint. The increased force transmission at this joint in combination with thoracic kyphosis limits the ability of the ribs to expand during respiration and the respiratory muscles to properly function thus reducing lung volume and blood oxygenation.
Collectively, core strength imbalances may be associated with or predispose an individual to injury. Successful preventative strategies include modifying training schedules or external body support (i.e., patellar knee brace, footwear, lumbar brace) (Yeung & Yeung, 2009). However, it has been shown that appropriate muscular balance exercises enhance the joint range of motion. As just one example, gluteus medius muscle strengthening exercises reduces the magnitude of frontal plane pelvic drop (Presswood et al., 2008), improves performance (Lephart et al., 2007) and reduces clinical symptoms in the soft tissues of the hip (Bolgla & Uhl, 2005), knee (Boling, Bolgla, Mattacola, Uhl, & Hosey, 2006; Mascal, Landel, & Powers, 2003; Nakagawa et al., 2008) and lumbar area (Nelson-Wong, Gregory, Winter, & Callaghan, 2008). Further, strength and kinematic improvements in the lumbar area are related to improvements in the thoracic area and leads to beneficial changes in shoulder and respiratory function.
In an attempt to prevent and/or heal injuries, taping has been classically employed. More recently, other compression products, such as the clothing described in European Patent 0834264, granted to Wacoal Corp. on Jun. 4, 2003, have also been introduced to simulate taping in a more convenient manner. In both cases, the approach is to hold or squeeze a joint or muscle into a certain position. Most therapists believe that a particular taping pattern will either enhance or inhibit the activation of the muscle; however, only inhibition has been shown in the research. As a result, atrophy or weakening of the muscle may be a concern.
Relatedly, compression products, such as those described in European Patent 0834264, aim to support the shoulder or glenohumeral joint. To do so, these compression products use bands on the shoulder in an attempt to anchor the scapula or shoulder blade at the top middle position, to counteract the shoulder rotating downwards. However, this configuration does not function as the arm reaches shoulder height, such as when throwing or other overhead movements. The configuration disclosed in European Patent 0834264 also tends to lead to internal rotation and anterior tilting of the scapula.
Conversely, shoulder and knee braces, orthotics, heel wedges and other orthopedic products have been introduced to redirect forces applied to the body and reduce pain and other clinical symptoms. Various braces are known that can mitigate some of the above challenges. However, braces tend to be uncomfortable, heavy, and aesthetically displeasing, especially when worn for long periods of time (e.g., a full day on the ski slopes). As a result, braces are often not worn for as long as they could be and thus their beneficial effects are not fully felt. Further, braces are used to immobilize or compensate for a change in joint stability or angular position caused by muscular weakness or injury and are thought to promote atrophy of the muscles surrounding the joint leading to secondary clinical problems.
There is therefore a need in the art for physiological support mechanisms that are lightweight, comfortable, and fashionable and that facilitate functional movement and muscular function of the kinetic chain. There is also a need in the art for a device that provides directional forces and a concurrent sensory inflow to the central nervous system to facilitate scapular stability by reducing scapular internal rotation and anterior tilting while allowing maximum range of motion and power generation of the upper kinetic chain. There is also a need in the art for physiological support mechanisms that provide optimal support of the seventeen muscles that attach to the scapula and the myofascial tracks that link posture, mobility and stability.